Unit 5: Heredity Flashcards
meiosis
process of cell division used in gamete formation; forms haploid (n) gametes from diploid (2n) parent cells, helping to maintain the proper number of chromosomes in the offspring
meiosis 1
consists of four stages: prophase I, metaphase I, anaphase I, and telophase I
prophase I
nuclear membrane breaks down and chromosomes condense and become visible; homologous chromosomes pair up and genetic recombination (crossing over) can occur
metaphase I
chromosomes line up in homologous pairs in the middle of the cell
anaphase I
pairs of homologous chromosomes separate (are pulled apart), number of chromosomes stays the same
telophase I & cytokinesis
two new nuclei are formed
meiosis II
consists of four stages: prophase II, metaphase II, anaphase II, and telophase II; is not preceded by DNA replication
prophase II
chromosomes again condense and become visible
metaphase II
chromosomes line up in a single line along the middle of the cell
anaphase II
sister chromatids separate and move to opposite ends of the cell; each sister chromatid will have its own centromere once this separation has occurred, making them chromosomes
telophase II
each of the two cells are split in half, resulting in four cells
how does meiosis generate genetic diversity?
1) in prophase I, homologous chromosomes pair up in synapsis to form tetrads, which allows them to cross over and exchange genetic info
2) in metaphase I, each pair of chromosomes lines up and assorts independently, with different parents having the paternal chromosomes on one side and the maternal chromosome on the other side
genes that are farther apart will have a ________ recombination frequency
higher
genes that are closer to each other will have a ______ recombination frequency
lower
linked genes
genes that are close together on the same chromosome tend to be inherited together more often, because their recombination frequency is lower
mendel’s law of segregation
an organism carries two variations of every trait (alleles), one from each parent, and these alleles segregate (separate) independently into gametes; this segregation occurs during anaphase I of meiosis when chromosomes are separated into separate gametes
mendel’s law of independent assortment
genes for different traits segregate independently one another; this independent assortment occurs during metaphase I of meiosis
genotype
genetic makeup or alleles for the trait in an organism
phenotype
physical expression of the genotype
homozygous
having two copies of the same allele for a trait (aa, AA)
heterozygous
having two different alleles for a trait (Aa)
dominant
requires only one copy of the allele for the trait to be expressed in the phenotype
recessive
requires two copies of the allele for the trait
monohybrid cross
cross where both parents are heterozygous for the trait
dihybrid cross
two organisms heterozygous for the same two traits are crossed
test cross
cross between an organism with a dominant phenotype and an organism with the recessive phenotype
autosomes
where most genes are located; chromosomes not directly involved in sex determination; males and females are equally likely to inherit genes on autosomes
sex chromosomes
involved in sex determination; genes on sex chromosomes have different inheritance patterns than those on autosomes; nonhomologous: females have two X chromosomes, while males have one X and one Y chromosomes
sex-linked genes
genes located on sex chromosomes
traits that are coded for by sex-linked recessive alleles are more likely to be expressed in ______ because they ________
males; only have one X chromosome
multiple gene inheritance
some traits are produced by multiple genes acting together to produce the phenotype; because more than one gene is involved in producing the trait, mendelian ratios do no tapply
nonnuclear inheritance
mitochondria and chloroplasts have their own DNA separate from nuclear DNA; this DNA does not follow the inheritance patterns found in nuclear DNA; these traits demonstrate maternal inheritance because the ovules are larger than the sperm, making them contribute more mitochondria and mtDNA than the sperm; the trait can be passed to either child from the mother but males do not pass the trait on
phenotypic plasticity
the ability of the same genotypes to produce different phenotypes in response to different environmental factors; the environment can affect gene expression and the resulting phenotype of an organism
